Also swinging an axe is like swinging a pick.+ if they ever need to go above surface where enemies might stay, they can cut down trees and shit to build barricades and whatever. An axe is infinitely more useful than a sword.

luffy's post time skip height is 174 cm (5'8½"), pre timeskip it was 172 cm (5'7½")
zoro was at 178 cm (5'10") before the timeskip, but became 181 cm (5'11½") over the timeskip
sanji was at 177 cm (5'9½") before the time skip, but grew to be 180 cm (5'11") over the timeskip

also, it should be noted that luffy grows to be 4 meters tall in 4th gear